The present invention generally relates to a method of reducing the antigenicity of vegetable proteins, while also improving the solubility characteristics of the vegetable proteins. More particularly, the present invention relates to a method of enzymatically hydrolyzing vegetable proteins, such as raw, natural soy proteins and denatured soy proteins, to reduce the antigenicity of the vegetable proteins while also improving the solubility characteristics of the vegetable proteins.
Over the years, researchers have found that soybeans may be processed to recover or extract a number of valuable components, such as soy protein and soybean oil, from the soy beans. Also, soybeans may be processed to form soy flours high in nutritionally beneficial substances, such as fiber and protein. Such processing of soybeans often include heat treatment for a variety of purposes, such as inactivating destructive enzymes or inactivating compounds responsible for off-flavors that are unpalatable to humans and/or animals.
Soybean processing techniques that employ heat frequently cause denaturation of proteins present in resulting soy component and products. The degree of protein denaturation depends upon the duration of heat and the temperature profile during the heating, among other factors. Additionally, some proteins in soybeans are more susceptible to denaturation at particular heating conditions than are other soybean proteins. Nonetheless, denaturation of soy proteins is problematic since denatured proteins typically exhibit greatly diminished solubility in water and aqueous solutions.
Many soy products, such as soy flour, soy flakes, and soy meal, are available and are commonly used for production of animal feeds and food products for human consumption. However, any such soy products that have been heat processed to a substantial degree have also undergone substantial soy protein denaturation and, consequently, frequently have a Protein Dispersability Index (subsequently referred to as “PDI”) on the order of about 20 or even less. The PDI is a measure of protein solubility (and consequently a measure of protein dispersability) in water. The PDI decreases as the level of protein denaturation in a soy component or product increases, absent further processing of the denatured protein to enhance the solubility of the denatured protein. Though there are vegetable protein products with relative high PDIs of 90 or more, and thus high levels of soluble proteins, these products are typically very expensive and/or often contain high levels of antigenic proteins.
Heat treating of soybeans and soybean components, although beneficial for deactivating destructive enzymes and compounds that contribute to unpalatable tastes, nevertheless do little, if anything, to reduce the antigenicity of the heat-processed soybean products. The antigenicity of a particular substance is directly correlated to the concentration of antigens present in the substance. Glycinin and β-conglycinin, which are commonly referred to as antigenic proteins, are two proteins in soybean products that cause the majority of the antigenicity typically observed in soybean products. Consequently, glycinin and β-conglycinin, by their presence or absence, predominantly control the level of antigenicity of a particular soybean product.
Heat-treating and heat-processing typically do not sufficiently reduce the concentration of antigenic proteins, such as glycinin and β-conglycinin, in a particular proteinaceous material. Other soybean processing techniques exist that may or may not incorporate heat treatment steps. For example, some commercial processing plants employ organic solvents, such as hexane, to extract oil from soy beans or soy products, such as soy flakes. The heat that is applied during the oil extraction process causes some denaturation of protein in the soy products. The heat is typically employed during the oil extraction process for purposes of evaporating the organic solvent. This heating for solvent evaporation purposes may cause some reduction of the antigenic protein concentration, though any such reduction is only an insignificant reduction. The organic solvent, such as hexane, that is employed in these processes for oil extraction purposes typically does not cause the destruction or removal of antigenic proteins, such as glycinin and β-conglycinin. There are other organic solvents that may be employed in these processes for purposes other than oil extraction. Some of these other organic solvents may even bring about significant reductions of the concentration of antigenic proteins, such as glycinin and β-conglycinin, in a particular proteinaceous material.
The destruction of antigenic protein that provides a reduced level of antigenicity in soybean products is important, since antigens, such as antigenic proteins, when introduced into a human being or into an animal, frequently cause production of antibodies that lead to development of allergic reactions that in turn reduce the digestibility of soybean products or cause other nutritional disturbances. Thus, to reduce the opportunity for allergic reactions, it is beneficial to reduce the antigenicity of soybean products by reducing the concentration of antigenic proteins, such as glycinin and β-conglycinin, in the soybean products.
However, soybean processing techniques that rely on organic solvents, even though beneficial for destruction of antigenic proteins, are not an optimum solution to the antigenicity issue. First, reducing the antigenicity of soybean products using such solvent-based processing techniques nevertheless typically leaves the soybean products with high levels of denatured proteins. These high levels of denatured proteins contribute to poor protein solubility characteristics in soybean products produced by solvent-based processing techniques. Furthermore, complete removal of the organic solvent from soybean products produced by solvent-based processing techniques is challenging and often incomplete, since trace levels of the organic solvent typically remain in the soybean product. Consumers are increasingly aware of research studies that raise questions about the effects of trace levels of organic solvents on human health. Therefore, to raise public perception of food quality, it is useful to minimize or even eliminate use of organic solvents in food processing techniques.
However, other than solvent-based processing techniques, heat-based processing techniques that denature proteins while leaving antigenic proteins intact or substantially intact are the most common soybean processing techniques. Furthermore, other processing techniques, such as grinding or milling, though not relying upon heating that denatures proteins, nevertheless, typically leave high and substantial levels of antigenic protein in the processed soybean components.
Thus, there is a need in the food and animal feed manufacturing industries for a technique of processing vegetable protein sources, such as soybeans and soybean components, that reduces the antigenicity in soybean products to reduce the potential for allergic reactions in humans and animals that consume the soybean products. Furthermore, there is a need for a food and animal feed processing technique that improves the solubility, and thus the dispersability, of denatured proteins in vegetable sources of protein, such as soybean products. Enhanced solubility and dispersability of denatured proteins is necessary to allow production of beverages, such as milk substitutes, milk replacers, and infant formulas, that contain proteins derived from vegetable sources, such as soybeans, and to support production of food products and animal feeds that incorporate dispersed or emulsified proteins derived from vegetable sources, such as soybeans. The process of the present invention provides an optimum solution to these needs by providing a product with proteins exhibiting high levels of solubility where the product also contains minimal, if any, levels of antigenic proteins.